| Along with the pace of speeding up basic operational capability construction initiated by China Meteorological Adminstration, multiple regional automatic meteorological stations and synthetic receiving satellite stations have been successfully built and operated in west of Southern Xinjiang in recent years. Meanwhile, a Doppler radar station has been built in2007and is operationally running since then. All this measures have greatly improved forecast capability for hail weather in west of Southern Xinjiang. By collecting and digging into52a time series data of meteorological hail between1962-2013, hail disaster reports material from13counties and data from sounding station located in west of Xinjiang, and in cooperated with MICAPS regular meteorological data, regional automatic meteorology station data, we analyzed spatial and temporal distribution of52a hail weather and its environmental characteristics, then pointed out occurrences pattern in climate point of view. We also analyzed application of Doppler radar data and satellite products in hail weather prediction and reached the preliminary results about Doppler radar character of hail weather. In addition, we deeply explored the environmental background, sounding indicator, radar echo characteristic physical mechanism and evolving pattern of strong hail weather process occurred in23, May of2012and18, June of2013. The main conclusions are listed below:Spatial and temporal distribution of hail weather and environmental characteristics:days of hail weather in west of Southern Xinjiang illustrates a trend of increasing, in-year hail weather behaves a significant oscillating characteristics; spatial distribution varies apparently, general trend is more lives on the North while less on the South; local hail weather is obviously more than systematic hail weather. Season when hail weather takes places in concentrated in May-July and therefore shows a unimodal shape. Vertical shear, humid convective energy and entire layer water vapor integral must simultaneously satisfy certain criteria before hail weather takes place. When vertical shear is bigger (>15m/s), it has positive contribution to occurrence of hail of D>10mm. More or less of water vapor has little effect on hail occurrence, but when hail weather occurs, if there exists weak vertical shear (≤12m/s) and low CAPE (CAPE<100J·kg-1), then bigger entire water vapor integral contribute positively to small hail, if there exists strong vertical shear (> 15m/s) and high CAPE(CAPE>300J·kg-1), then bigger entire water vapor integral (IQ>2000) contribute positively to big hail. Suitable0℃layer height (3830～4256m in average) and-20℃layer height (6628～7717m in average) contribute positively to produce hail; The less the thickness between0℃-20℃layer the more suitable for bigger hail occurrence. The main weather types are Central Asia trough (vortex), unstable shortwave trough and the south-north superimposed trough type III, Central Asia trough (vortex), and over-passed unstable shortwave trough. These weather types are important systems to trigger systematic hail and local hail. The central Asia trough (vortex) occurs the most frequently, among them the southern trough (vortex) accounts for50%of the total amount; unstable shortwave trough occurs less, superimposed North and South trough occurs the least. Analysis on hail weather trigger mechanism found that cold vortex, low trough, shear line, topographic lifting and so on can all trigger hailstorm. West of Southern Xinjiang has complicated terrain. West, north, south side of it are surrounded by mountains and companioned by desert, oasis, Gobi basin so it is easy to produce strong local convective weather, special "inverted trumpet" topography pours the cold air from the west to the East into the basin which shapes a "cold pool" to uplift the terrain.Doppler echo features for discriminating hails of different diameter:Radar product features for small hail weather:ordinary monomers, the multi cell storm, squall line, with a high centroid, rear inflow notch (RIN), high-level echo overhang and mesocyclone weak, weak echo region and C-VIL jumped, the maximum liquid water content threshold of45kg/m2.Radar product features for large hail weather:super monomer, with type V echo, high center of gravity, rear inflow notch (RIN), high-level echo overhang and strong mesocyclone, obvious bounded weak echo region (BWER) and C-VIL jump, high water content of liquid increase (threshold≥60kg/m2).According to three kinds of information on Hail Detection Algorithm (HDA), i.e. POH (any size hail probability), POSH (strong hail probability) and MEHS (maximum expected hail size), by comparing and evaluation using default parameters of HDA algorithm on14hailstorm process17echo monomer, we adjusted the related parameters and then evaluate the effect again. In this way, the adjustment effect is improved obviously.By analyzing the evolution of strong echo of hailstorm center we found there are mainly four paths that can influence South Western hailstorm:the first one is the northwest path, which occurs the most frequently; the second is the north route, the third is the west route; the fourth is the newborn convective cells.By analyzing strong hail weather processes taken place in west of Southern Xinjiang in May 23,2012and June18,2013using multiple kinds of meteorological data, the following is found: Hail weather process in May23,2012spread a rarely seen wide range, often known as meso-y scale convective system. Heterogeneous surface heat and distribution of water vapor is the main reason for the occurrence of this strong convection weather. Thermal effect of Hail weather is obvious, the thermodynamic parameters of CAPE and LI value center fit well with regions where hail weather takes place, and CAPE (LI) increases with time (reduce); Weak vertical wind shear, vertical vorticity and slantwise vorticity development (SVD), are the stratification characteristics which cause massive hailstorm; Linear multi cell storm, low layer weak echo region (WER), low reflectivity and high gradient zone are the main characteristics of echo, jumping VIL has indicator meaning for nowcasting of Hail weather in West of Southern Xinjiang.In June18,2013, hail weather was taken place where weather system is influenced by the mesoscale convective system (MCS), overpassed Bashan Lake vortex was weakening and large circulation background was in favor of lower shear line; Maintains of the convective instability and strong vertical wind shear in the lower troposphere atmosphere, plenty of water vapor, appropriate height of feature level are important conditions for the development of strong hail storm; increasing convective available potential energy, decreasing LI index are significant indicators of strong hail, NCAPE maximum time is close to hail time; Strong hailstorm has characteristic hail cloud and supercell, single super long time maintenance is one of the important reasons of Hail whose diameter is bigger than6cm. TITAN tracking forecast has indicator meaning in predicting supercell Storm shift in this hailstorm weather.This research is helpful to improve the prediction of hail weather in west of Southern Xinjiang, a comprehensive understanding of hail weather in west of Southern Xinjiang lay consolidated ground for further study on hail weather forecast and artificial hail suppression. |
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